The present invention relates to the fabrication of dielectric waveguides and, more particularly, to a method of designing a waveguide of the type which is to propagate at least two different frequencies of optical energy. The waveguide is manufactured so that the phase mismatch between the two frequencies of optical energy has little or no first order dependence on the dimensions of the waveguide.
Dielectric waveguides, such as solid state waveguides, are used to couple energy from one frequency to another. Such solid state coupling is used for various purposes, including frequency doubling. Problems arise, though, if there are variations in the difference in the phase velocity of the corresponding modes of the waves being coupled. The amount of energy coupled between the waves is dependent upon the phase match between the two waves. In other words, the output power created by a nonlinear interaction between two waves is dependent on the effective length of such interaction. This effective length is greatest in a dielectric waveguide when the waves are in phase with one another as they travel through the waveguide. The speed of a wave through such a waveguide and, hence, velocity phasematching between two waves in the same, however, is dependent upon the waveguide dimensions. This causes significant quality control problems in producing waveguides. In this connection, it will be recognized that since each wave transmitted by a waveguide will have a multitude of succeeding cycles, even a slight variation in the phase relationship between two waves can have a dramatic effect on the output power achieved from the nonlinear interaction and, in some instances, can result in no power coupling at all.